cGMP-dependent protein kinase and iron metabolism

cGMP依赖性蛋白激酶和铁代谢

• 批准号: 248173116
• 负责人: Professor Dr. Franz Hofmann
• 金额: --
• 依托单位: Institut für Pharmakologie und Toxikologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2016-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/248173116?language=en
• 关键词: cGMP; dependent; protein; kinase; iron

Iron is a vital metal ion required for the proper function of essential proteins and a critical element in many cellular functions. Iron is resorbed mostly by the duodenal enterocytes, is then transported in the blood by transferrin, and stored bound to ferritin in liver, bone marrow, erythroblasts, and skeletal muscle. Hemoglobin contains about half of the bodys iron. Iron absorption is tightly regulated in the intestine and controlled by the hepatic factor hepcidin. Hepcidin inhibits the iron exporter ferroportin present in macrophages and at the basolateral side of the enterocyte. The transcription of hepcidin is stimulated by proinflammatory cytokines such as IL-6, and inhibited by hypoxia, erythropoietin, and lack of iron. We have generated mouse lines that express cGKIa or cGKIb under the SM22a promoter in smooth muscle cells (rescue mice). Analysis of these mice and conventional knock-out mice revealed that cGKI-/- or cGKI rescue mice develop a bleeding ulcus duodeni, anemia and a severe deficit of iron. The decreased iron availability resulted in a decreased hemoglobin concentration and erythrocyte content. The same animals had significantly elevated plasma levels of reticulocytes and erythropoietin supporting the notion that the cGKI modified mice had an iron-deficiency anemia. We were unable to rescue the phenotype in the rescue animals by i.m. injection of iron. cGKI-/- mice show enhanced apoptosis of erythrocytes in the spleen. However, premature apoptosis of the erythrocytes in the spleen would not explain the very low iron content of the spleen, because erythrocytes are degraded in macrophages, which store the iron released during hemoglobin degradation and provide it for the resynthesis of hemoglobin. In agreement with these results, untreated cGKI rescue mice had elevated mRNA expression of the transferrin receptor and of the divalent metal ion transporter in the spleen suggesting the iron deficiency is sensed by the reticuloendothelial cells of the spleen. As expected, the iron storage protein ferritin is reduced to nearly zero level in the spleen of untreated cGKI mouse lines and does increase only slightly with the injection of iron. These results are indicative of an iron absorption/storage deficit of the spleen macrophages.Preliminary data show that cGKI-/- and the cGKI rescue mice have anemia caused by a severe iron deficit in the spleen. Oral or i.m. supplementation of iron has not restored the spleen iron deficit nor the anemia. Very preliminary data even suggest that treatment of the animals with PPIs that prolongs dramatically the live span of a subset of the cGKI-/- mice does not change the anemia. Goal of this project is to understand at which level cGKI affects the iron metabolism, because so far no interaction between iron metabolism and cGKI has been reported.

铁是一种重要的金属离子，是必需蛋白质正常运作所必需的，也是许多细胞功能的关键元素。铁主要由十二指肠肠细胞吸收，然后通过转铁蛋白在血液中运输，并与铁蛋白结合储存在肝脏、骨髓、红细胞和骨骼肌中。血红蛋白含有人体大约一半的铁。铁的吸收在肠内受到严格的调节，并受肝因子hepcidin的控制。Hepcidin抑制存在于巨噬细胞和肠细胞基底外侧的铁输出蛋白铁转运蛋白。促炎细胞因子如IL-6可刺激hepcidin的转录，而缺氧、促红细胞生成素和缺铁可抑制hepcidin的转录。我们在平滑肌细胞中生成了SM22a启动子下表达cGKIa或cGKIb的小鼠品系（拯救小鼠）。对这些小鼠和常规敲除小鼠的分析显示，cGKI-/-或cGKI拯救小鼠出现十二指肠溃疡出血、贫血和严重的铁缺乏。铁可用性降低导致血红蛋白浓度和红细胞含量降低。同样的动物血浆中网状红细胞和促红细胞生成素水平显著升高，这支持了cGKI修饰小鼠患有缺铁性贫血的观点。我们无法通过注射铁来挽救被拯救动物的表型。cGKI-/-小鼠脾脏红细胞凋亡增强。然而，脾脏红细胞过早凋亡并不能解释脾脏铁含量很低的原因，因为红细胞在巨噬细胞中被降解，巨噬细胞储存血红蛋白降解过程中释放的铁，并为血红蛋白的再合成提供铁。与这些结果一致的是，未经处理的cGKI救援小鼠脾脏中转铁蛋白受体和二价金属离子转运体的mRNA表达升高，表明脾脏网状内皮细胞可以感知铁缺乏。正如预期的那样，在未处理的cGKI小鼠脾脏中，铁储存蛋白铁蛋白降低到几乎为零的水平，并且在注射铁后仅略有增加。这些结果表明脾脏巨噬细胞铁的吸收/储存缺陷。初步数据显示，cGKI-/-和cGKI拯救小鼠有由脾脏严重缺铁引起的贫血。口服或静脉补充铁不能恢复脾铁不足或贫血。非常初步的数据甚至表明，用PPIs治疗动物，显著延长了一部分cGKI-/-小鼠的寿命，但并没有改变贫血。该项目的目的是了解cGKI在哪个水平上影响铁代谢，因为到目前为止还没有报道铁代谢与cGKI之间的相互作用。